When a projection display apparatus is projecting an image light onto a screen, the projection may be temporarily interrupted according to operation which is entered by a user. A projection display apparatus has been discussed in which the amount of lamp power that is supplied to a lamp is reduced in order to conserve electrical power during periods when the projection is interrupted. The configuration of such a projection display apparatus is illustrated in FIG. 1.
The projection display apparatus illustrated in FIG. 1 comprises power source 11, ballast 12, lamp 13, image signal controller 14, display element 15, and light intensity controller 16. In FIG. 1, an outline arrow indicates a light flux.
Ballast 12 adjusts the lamp power that is supplied from power source 11 to lamp 13 in accordance with a control signal received from light intensity controller 16. Lamp 13 is lighted by a lamp power supplied from power source 11 via ballast, and illuminates display element 15.
Image signal controller 14 receives an image signal from the outside and provides the image signal to display element 15. Display element 15 displays an image indicated by the image signal received from image signal controller 14. Display element 15 may be, for example, a liquid crystal element that is sandwiched by deflection plates in the form of crossed Nichol prism.
By being illuminated by the light emitted from lamp 13, an image light emitted from display element 15 is projected onto screen 20.
Light intensity controller 16 receives an interrupt operation to interrupt projection which is entered by the user. When the interrupt operation is entered, light intensity controller 16 instructs image signal controller 14 to cause display element 15 to display a full-black image. By performing a control to display a full-black image on display element 15, light emitted from lamp 13 is unable to reach screen 20, thus interrupting the projection. In the following, a state in which projection is interrupted is called “an image mute state”, and a state other than the image mute state is called “a normal lighting state”.
When the interrupt operation is entered, light intensity controller 16 also provides a control signal to ballast 12 such that lamp power that is lower than lamp power at the normal lighting state is supplied to lamp 12.
Projection display apparatus 10 described above achieves power saving because during the interruption of projection, low-power lighting is performed in which lamp 13 is lighted up with lamp power whose level is lower than the level during a normal lighting state.
Typically, a lamp of a projection display apparatus is a discharge lamp. Accordingly, lighting a lamp at a lamp power that is lower than a predetermined power (rated power) causes unstable light emission and damages the electrode and luminous tube of the lamp.
Thus, Patent Document 1 (JP2009-093862A) discloses a technique in which, if the lamp power is lower than the rated power for a certain period of time or longer, then a lamp refreshing process is carried out to temporarily increase the lamp power at the appropriate time interval. According to this technique, even if lighting a lamp at a lamp power that is lower than the rated power damages the electrode and the luminous tube of the lamp, the lamp refreshing process can return the states of the electrode and the luminous tube to normal states.